In most fires, flames and smoke are generated almost at the same time, and sometimes the smoke may be generated firstly and followed by the occurrence of flames. In some fires, burning of some substances only generates the smoke without flames. Therefore, the smoke detection is a very important issue for fire prevention and rescue. When using a smoke detecting system, a fire can be reported at its early stage so that the early fire fighting may be proceeded to reduce the casualties.
The conventional smoke detecting devices, e.g. a photoelectric smoke detector and an air sampling smoke detector, use the physical properties resulting from increase of the smoke particles as the basis of fire detection. The photoelectric smoke detector emits the light, and the light is scattered and the brightness is changed when smoke particles exist in the air. Because the photoelectric smoke detector detects the variation of the brightness by light emitting to determine if there is a fire, the detecting range thereof is restricted. Therefore, the smoke detecting in large areas by the photoelectric smoke detector may not be effective. The air sampling smoke detector collects the air sample in the detecting area and analyzes the elements of the collected air to determine if there is a fire. To collect the air sample, the air sampling smoke detector must be equipped with a duct system for facilitating the detection. Besides, the sensors of the air sampling smoke detector are very expensive.
Accordingly, the conventional smoke detecting devices have the shortcomings as follows: 1) it is hard to detect a smoke in high and large-area buildings, such as the factories, the stadiums and the shopping malls, thereby wasting the early rescuing time; 2) the accuracy thereof is too low, thereby causing too many false alarms; and 3) a large number of sensors, ducts and controlling systems needs to be installed, thereby raising the cost.
Therefore, for improving the accuracy of the smoke detecting device and reducing the cost, the visual smoke detecting device has been recently developed, which identifies if there is any object whose features meet the fire smoke by using the original monitoring system in a building. Once the smoke detecting device determines the object as the fire smoke, an alarm will be generated. Such visual smoke detecting devices are designed to use many parameters relating to the features of a smoke to be analyzed, so as to make the smoke detection quick and accurate. For example, Taiwan Patent No. 535956 discloses a visual smoke detecting device for processing images and generating digital determination signals via a digital signal processing device, and Taiwan Patent Pub. No. 200617814 discloses a method and system for detecting fire by capturing images in a monitored area with an image capturing device, detecting whether an image difference is generated in the captured images by determining shades of color thereof, comparing the image difference with features of a flame or a smoke, and determining if a fire exists or is enlarged based on the comparison result. However, other parameters for precisely detecting a smoke are not applied in these patents, so the mentioned smoke detecting methods and devices will easily generate false alarms.